Governmental bodies control access to radio frequency spectrum. In some cases radio frequency spectrum is reserved for unlicensed communications. For example, in the United States the government has reserved the 902-928 MHz and 2400-2483.5 MHz frequency bands (commonly referred to as the Industrial, Scientific and Medical (ISM) frequency bands) for unlicensed communications. Thus, Bluetooth wireless communication devices can operate on the ISM frequency bands without requiring a license for such communications.
Other radio frequency spectrum is licensed by governments, for example, by auctions to particular operators. While sets of frequency bands may be reserved for certain types of licensed communications, not all of the frequencies within the band may be used within all geographic areas. For example, certain frequencies within the ultra-high frequency (UHF) band are reserved for analog television broadcasts, but not all geographic locations include licenses for all of the reserved frequencies. Thus, while the 470-512 MHz frequencies are reserved for analog television channels 14-20, any particular geographic area will typically include only one of two television channels using these reserved frequencies.